There are various enzyme-based cleaners on the market for this purpose. You can usually find them at places like home improvement stores (Lowe's, HD). They are typically concentrates you dilute and spray on, allow to sit for a period of time then hose and brush off. About as much time and effort as involved as power washing, all in all :-)

Using a bleach solution works well also but poses some issues with the environment - at least the immediate environment. The enzymes are totally safe.

As you might tell, I have the same issues. With our moist winters, concrete surfaces that are not in a full open exposure tend to grow some serious crops of algae over winter. And older pavers or exposed aggregate surfaces seem to do a better job of hosting them than smooth finishes. Sealing the surface might be the only long term solution.

Thanks for this. It's an annual thing for us here and it just looks so nasty. One year, I had a big bottle of detol and used it on a north facing brick wall and it stayed ok for a few years. I was hoping there was a magic bullet but, sigh, I don't think there is. Oh well, misery loves company and I bet we have lots of company in this PNW!

My cedar deck is slimy and green. Especially between the door to the bedroom and the hot tub. ICK.